Whorl and stalk damage by European and Southwestern corn borers to four events of Bacillus thuringiensis transgenic maize

Twenty-eight transgenic maize hybrids producing the Bacillus thuringiensis (Bt) endotoxin (Cry1A(b) or Cry9c) and several of their non-Bt isolines were evaluated for control of the southwestern corn borer, Diatraea grandiosella Dyar, and the European corn borer, Ostrinia nubilalis (Hubner). The Pt hybrids represented four events (Mon810 [Cry1A(b)], Bt11 [Cry1A(b)], 176 [Cry1A(b)], and CBH354 [Cry9c]) from seven seed companies. Maize hybrids were grown in four locations ranging from the northern to the southern Texas Panhandle, a semi-arid environment with hot days, cool nights and < 220 mm of rain during the growing season. Maize was infested with each species of corn borer using the Davis applicator at the mid-whorl (first-generation borer) and tassel (second-generation borer) growth stages. All Bt hybrids controlled first generation infestations of both species of corn borers. In contrast, second-generation corn borers were controlled well only by maize with the Mon810, Bt11, or CBH354 events. Second-generation corn borer control by event 176 hybrids was not adequate when compared with the other events. Percentage infestation, larval survival, and damage to most of the event 176 hybrids by second-generation corn borers was similar to non-Pt hybrids. Second-generation SWCB larvae surviving on event 176 were weighed and their survival through the winter (January - March) was monitored. Larvae collected from root crowns of event 176 hybrids weighed the same as those surviving on a non-Bt hybrid from Novartis. SWCB larvae survived the winter equally well in maize stalks of transgenic and non-Pt plants. Yields were not significantly enhanced by control of corn borers by the Bt hybrids. (C) 2000 Elsevier Science Ltd. All rights reserved.